Metal coating of long lengths of metal bodies



Jam 4, 1966 K. I-I. BAEssLER ETAI. 3,227,577

METAL COATING OF LONG LENGTHS OF METAL BODIES Filed Sept. 18, 1962 4Sheets-Sheet 1 HYDROGEN 3837 FIG. I

METAL COA'IING OF LONG LENGTHS OF METAL BODIES Filed sept. 18, 1962' Ja-4, 1956 K. H. BAESSLER ETAL 4 Sheets-Sheet 2 .rom E32-E344 Jm mJE32-2344 2950.2

Jan' 4, 1966 K. H. BAESSLER ETAL 3,227,577

METAL COATING LONG LENGTHS OF METAL BODIES Filed Sept. 18, 1962 4Sheets-Sheet 5 WIRE FROM THERMOSTAT APPLICATOR ARRANGED TO W l2\} T TURNON HEATER 62a IF TEMPERATURE IS LOW,OR COLD 63 WATER IF TEMP- Q ERATUREls HYDROGEN HIGH @D i ,|19 w TEMPERATURE Jan- 4, 1965 K. H. BAr-:ssLERETAL 3,227,577

METAL COTING OF LONG LENGTHS OF METAL BODIES Filed sept. 18, 1962 4Sheets-Sheet 4 T .m R S RE m w um R m .E M F 2 WH/ T R F B F. 4 L V 3 EU0 0 2 RB DE wE El mw Mm .H O N PS Cw E 4 3 cMN... Ml E O 3 T5 UT R m 2 2NA D W W E Y D 2 o UR H E O O O 1. LI .m 2 2,2 M Aw 02 L. W k m L.; 2`E1; w m 2 ww EL 1 www S 2l 5 En G. 2 M Il v .m Tw... AP ww ms 1(\ UnitedStates Patent O 3,227,577 METAL `ClOAllNG F LQNS LENGTHS 0F METALL BDlESKarl Hurst Eaessler, Walnut Creek, Calif., and Harry Robert Gardner,Jr., Trenton, Howard .lohnson- Godfrey, Pennington, and Dartrey Lewis,Trenton, NJ., assignors to The Colorado Fuel and lron Corporation,

Denver, Colo., a corporation of Colorado Filed Sept. 1S, 1962, Ser. No.224,349 18 Claims. .(Cl. 117-102) This invention relates to coating oflong lengths of metal bodies, such as wire and strip, with molten metal;the molten metal being caused to solidify to form a coating on the metalbodies. More particularly the invention relates to coating long lengthsof metal wire or strip with molten aluminum and causing the moltenaluminum to solidify as a coating upon the wire or strip.

According to the invention the metal strand to be coated with a coatingmetal is passed through an aperture die in a bath of the molten coatingmetal; the aperture in the die being slightly larger than the crosssection of the strand so that as the strand passes through the die theouter surface of the strand is in contact with molten metal occuping theannular space between the strand and wall of the die and simultaneouslyas the strand continuously moves through, and outwardly from the die,the thickness of molten coating adhering to the strand may be controlledby a confined fluid pressure, i.e. static pressure, applied at theoutlet end of the die against the molten metal in said annular space ina direction opposite to the direction of travel of the strand.

The process of the invention will hereinafter be described in connectionwith typical embodiments involving the coating of steel wire withaluminum but it will be understood that the principles of the processmay be used for coating of metal products other than steel wire withmolten metals other than aluminum, such as, for eX- ample, coating withzinc, zinc containing minor amounts of aluminum, tin, alloys ofaluminum, and the like.

In general, the process of this invention, according to one manner ofcarrying it out, involves thorough cleaning of the steel wire, andremoving any oxide if present on the surface by heating it in a hydrogenatmosphere or by other suitable method, and then passing it into a bathof molten aluminum, preferably in a downward direction, and out of thebath through a die which serves to control the ow of the molten aluminumonto the surface of the wire as a concentric coating of uniform andcontrolled thickness. After emerging from the aluminum bath the wire ispassed, preferably in a downward direction, through an elongate chambercontaining a gas, preferably a non-oxidizing gas such as hydrogen, underpressure which also serves to control thickness and surfacecharacteristics of the coating, and then through a cooling bath,preferably water, under controlled conditions to further cool andsolidify the coating. The wire emerges from the cooling bath as aluminumcoated wire.

The invention also provides certain novel method steps and apparatuswhich is useful in carrying out the steps of the process, as describedin further detail hereinafter.

Although the novel features which are believed to be characteristic ofthe invention are pointed out in the annexed claims, the inventionitself as to its objects and advantages and the manner in which it maybe carried out may be better understood by reference to the followingmore detailed description, taken in connection with the accompanyingdrawings, forming a. part hereof, in which FIG. 1 is a view primarilydiagrammatic showing apparatus and illustrating the various steps forcarrying out the process of the invention;

3,227,577 Patented Jan. 4, 1966 lFlGf.. 2 is a partial andsemi-diagrammatic sectional View on a larger scale showing the apparatusfor passing the wire in a guided path downwardly through the moltenaluminum 'bath and more particularly the coating die arrangement forcontrolling the flow of molten aluminum onto the wire;

FIG. 3 is a view somewhat similar to FlG. 2, but showing a modifiedform, including a wire guide and floating die',

FIG. '4 is a partial and semi-diagrammatic sectional view of a modifiedform of cooling apparatus for cooling the coated wire after the moltencoating has been applied; and

FIG. 5 is a partial 'and semi-diagrammatic sectional View of a differentform of apparatus for controlled cooling of the lwire after the moltenaluminum coating has been applied.

Referring now to the drawings, in which like reference characters denotelike parts throughout the several views, the cleaning apparatussometimes called the cleaning line and the other units of one form ofplant for practicing the invention are shown diagrammatically in FIG. 1.As shown, there is a payoff reel, or swift 11 upon which the wire to becoated is wound and from which it is unwound and passed continuouslythrough the various units of the plant where various treating steps arecarried out. The wire, designated generally by reference character NV,after passing through the system is finally wound on a driven reel ortake-up block 12. It will be understood that the block is equipped withthe necessary guide rolls, driving mechanism, indicators and otherequipment known to those skilled in the art. rl`he wire W in its variousstages as it proceeds successively through the various units of theapparatus is designated by refe-rence character W coupled with anidentifying numeral, as for example: W1, W2 etc. The wire W in theillustrative embodiment is steel wire having a diameter of 0.146 whichwas drawn from hot rolled rod stock made from carbon steel havingspecifications as follows: C O20-0.25%, Mn .20-.55%, P 0.040% max., S0.050% max. lt will be understood that the specification of the wire isgiven `as one illustrative example.

In the process as illustrated, the wire W1 from reel 11 passes through atank 13 containing a molten lead bath 13a maintained at about 850 F. todecompose soap which has been picked up by the wire from the dies in theprevious drawing operation. The emerging wire W2 passes through a Waterdip' 14a in tank 14 to partially cool the wire before it enters ahydrochloric acid bath 15a in tank 15. The hydrochloric acid bath ismaintained at about 15% acid and at about 130 F. Til-ence the wire W4passes through a cold water wash 16a in tank 16.

The emerging wire W5 then passes through alternating anodic, cathodicand anodic cold sulfuric acid baths 17a, 18e, 19a respectively in tanks17, 18, 19, the electrolysis system `being designatedby referencenumeral 20. The sulfuric acid is approximately 50% by volume yat atemperature maintained preferably between F. and 100 F. An anodiccurrent of about 1500 xcoulom'bs per square foot is maintained. The wireW6 is then w-ashed in hot water 21a maintained at about 150 F. in tank21. The emerging wire W7 is then 1subjected to an ultrasonic water wash22a :at about 150 F. in tank 22. The ultrasonic wash consists -ofapplying 1000 watts per wire at about 40 kilocycles frequency. Theemerging wire W8 is `then dried in hot air dryer 23. The construction ofsuitable cleaning apparatus as mentioned above is known to those skilledin the art.

lt is essential that the cleaning steps employed produce a chemicallyclean `surface on the wire which is free from dirt, smut or othercontaminating substances. However, in some instances the cleaning neednot be done exactly as described Iabove. For example, an alkali cleanermay be substituted for the hot lead bath, or the wire may be heated in afurnace yto decompose the soap film on the wire. If the soap on the wirewhich may have been picked up in the prior wire drawing opera-tions isnot -too heavy the hot lead may be omitted. Also, the hydrochloric acidstep may be omitted if the wire has been cold drawn and is reasonablyfree from excessive soap, scale or rust. The anodic sulfuric acidcleaning step is useful for removing carbonaceous smut from lthe surfaceof the wire. The ultrasonic cleaning is useful for removing loose dirtfrom the wire surface and to some extent serves the same purpose as theanodic sulfuric acid. One or more of these steps may be omitted ifotherwise the wire is thoroughly cleaned. The significant point is thatthe cleaning steps produce a wire surface that is thoroughly free fromdirt, smut, or other con- -t-aminating substances.

After thorough cleaning, the Wire is heated in hydrogen to a temperaturebetween 1300 F. and 1800 F. The purpose of heating in hydrogen is toreact with any i-ron oxide film, that may be present on the surface `ofthe wire to reduce the iron oxide to be metallic iron. If desired, thewire may be exposed to air during the early stages of raising itstemperature to the range stated above, so that a visible (yellow, blueor gray) oxide film is formed on the wire. Then when the wire issufficiently hot the oxide film is then reduced to iron by the hydrogen.The hydrogen is preferably passed in a confined stream enveloping thewire and in a direction -counter to the direct-ion of the movement ofthe wire. Preferably, the hydrogen is introduced at a point near thesurface of the molten aluminum bath through which the wire passes inadownward direction, as described in further detail hereinafter. Thesignificant point is that the surface of the wire be thoroughly cleanedand freed from oxides or other contaminant-s.

As illustrated in the drawings, t-he wire is heated by passing anelectric current through the wire while exposing the wire to a hydrogenatmosphere. In the arrangement shown, one phase a of a three-phasesupply is connected with the travelling wire at and 25a by means ofcontact pulleys 26, 26a. The other two phases b and c are connected withthe wire Iat intermediate points 27 and 2S by similar contact pulleys27b and 28C. This arrangement constitutes a delta -three-phase circuitin which the wire W9 forms the connection between the three phases.Since the portion of the wire entering and the portion of wire leavingthe heating zone are both at the same potential and since the wire atIthese points is connected to grounded objects, there is no potentialabove ground on the payoff lor take-up reels. Other methods of heatingthe wire may be employed, if desired. For example, the wire may beheated in a tube furnace.

In the apparatus, as shown, the wire during heating is passed through anelongate heating tube having a confining wall '30; thus provid-ing atunnel 31 through which `the wire may travel while hydrogen may be andis, passed in a counter direction in a confined stream enveloping ythewire. The wire passes over a pulley 32 mounted in the tunnel and thencein -a downward direction, through a vertically disposed length 33 of thetubular tunnel 31. This forms a pipe section 34 of lthe tunnel whichextends into the chamber 35 of a heated furnace 36 which contains a potof molten aluminum. The vertical section 33 of the tunnel is providedwith connecting hollow conduit 37 which 'is connected -to a source 60 ofhydrogen under pressure. 'This conduit 37 provides a port 38 near thesurface 39 of the molten aluminum 40 in furnace 36, later -to bedescribed. It will be observed that the lower end 41 of the verticaltube section 33 extends to 'a point below the surface 39 of the moltenaluminum bath 40. Thus, hydrogen under pressure introduced through port38 will be constrained to dow through the tunnel in a direction counterto the direction of travel of the wire. The hydrogen may be ventedthrough a wire guide or aperture 42, in the closure piece 43 or throughother suitable vent mean-s at the forward end of the tunnel 31.

After heating the wire and while it is still enveloped in a hydrogenatmosphere, the wire W10 passes over rotatably pulley 32 and thencedownwardly through the tube section 33 which may be in the form of apipe. The wire then passes vertically downward int-o the molten aluminum40, entering the bath at a point below the surface 39 rof the moltenaluminum. The distance between the wire heating zone and the aluminumba-th is chosen so that the wire W10 enters the molten aluminum 40 infurnace 36 at a temperature near to the tempera-ture of the moltenmetal, which is maintained at 'about 1275 F.

The aluminum bath 40 may be maintained at the required temperature byany suitable means. As shown in the illustrative embodiment (FIG. 1)this is done by heating elements 45, known in the art as Globar heatingelements. Preferably, the furnace 36, and as shown, is lined with aliner 46 of silicon carbide bonded with silicon nitride. Or the furnacemay beV lined with other suitable material which is not attacked by themolten aluminum. Solid or liquid aluminum may be added to the aluminumpot 36a in the furnace by any suitable means to maintain the level ofthe bath reasonably constant and to replenish molten aluminum that isremoved from the bath as the coating operation proceeds. As shown inFIG. 1, the aluminum is replenished by feeding aluminum rod 47 throughan appropriate aperture 48 in the furnace wall into the bath by drivenfeed rolls 49. If desired, the feed rolls may be driven automatically inresponse to a bath level sensing device in order to maintain a constantlevel of the molten bath 40.

The tube section 33, extends vertically downward through an appropriateaperture 50 in the roof 51 of the furnace, to a point 41 beneath thesurface 39 of the bath. A bafiie partition 52 having its lower edgeabove the bottom of the pot 46 and its upper edge above the surface ofthe bath permits clean aluminum only to pass underneath the baffle tothe coating section 53 of the pot.

The wire W10 passes downwardly through the molten aluminum in thecoating pot section 53 of the furnace and passes downwardly through anapplicator die 5S. The die, which is described in further detail lateron, permits the molten aluminum to ow downwardly from the aluminum potaround the wire in the form of a continuous coating which is attached tothe steel wire by alloying with it and the amount of coating is limitedby the size of the orifice 56 in the applicator die 55. As shown in FIG.1, the applicator die has an annular shoulder 57 from whichconcentrically depends a neck portion 57a fitting into a hollow boss 58depending from the bottom wall 59 of the furnace.

In coating steel wire of .146" diameter, for example, it has been foundthat if the thickness of the coating exceeds about .005, it is difficultto obtain a smooth coating. Also it is difficult to maintain an orificeon the applicator die having a diameter less than .010 larger than thewire diameter. However, it has been found that the hole or orificediameter in the applicator die can be increased to about .030 largerthan the wire diameter without obtaining an excessive flow of aluminumby applying hydrogen, or other suitable gas, confined under pressureagainst the outiiowing aluminum at the outlet end of the die as the wiretravels continuously through the die. For example, in coating wire ofthe size mentioned above, the preferred orifice 4size is .020" largerthan the wire diameter. For various sizes of wire the minimum orificesize is about 7% larger and the maximum orice size is about 21% largerthan the wire diameter, and the preferred orifice size is about 14%Vlarger than the wire diameter.

As shown in FIG. 1, hydrogen 60a under pressure, from a suitable source61 is introduced into pipe 62.

This pipe at its upper end is sealed around the boss 58 and dependsvertically downward' with its lower end below the surface 63 of a waterbathV 64' maintained in a suitable tank 65 located below the aluminumbath'. Thus, the upper end of the chamber providedr by pipe 62communicates with the annular space between the wire W2 and theperipheral boundary of the orifice S6 and the lower endv of this chambercommunicates with the water bath 64. This is described in further detaillater.

The coated aluminum Wire W12 travels downwardly within vertical pipe 62.Hydrogen is introduced into this pipe through a port 65a under sufhcientpressure to cause it tobubble out of the water 54 in tank o5. The gaspressure in pipe 62 is therefore maintainedr constant and equal to thehead 66 of water between the lower end 67 of the pipe and the surface ofthe water. The gas pressure in the pipe may, of course, be adjustablyvaried by raising or lowering the lower endv of the pipe' in relationtothe surface 63 of the water bath; for example, by raising or loweringthe surface of the water which may be done, by adjusting the height ofoverflow conduit 68 in the water tank.

It has been found that with a constant diameter orifice 56' in theapplicator die of about .020'H larger than the diameter of the wire(which in the case now being describedA is .146 diam.), the thickness ofthe aluminum coating on the wire can be controlledV by varying thepressure head e6. For example, with a molten aluminum bath in applicatorpot 53 which is 11/2 deep, the thickness of coating on` the .146 diam.wire may be varied between .0005 and .005 by changingy the head 66- froml to 4 of water pressure with a substantially constant linear travellingspeed' of the; wirev within the range of about 8O feet to 130 feet perminute. It will be understood, of course, thatY the hydrogen staticpressure in-pipe 62 is equal to the water head.

It has beenV found that the thickness of the coating depends upon thehead of molten aluminuml in the aluminum furnace above the level of theapplicator die, the clearance between the wire and the die, the lengthof the cylindrical portion of the die, the speed' of travel of the wire,aridthe back pressure exerted by the gas at the outlet end of the die.The back pressure ofthe gas counteracts the gravitational force orpressure of the molten metal due to its head in the furnace' and the'velocity head caused by the speed of travel of the wire as affected bythe length and width of the die oriiice. The back pressure may be variedbetween i) and 6 inches of water pressure according to the requiredcoating thickness for a 11/2 head of molten aluminum in the furnace. lfa deeper aluminum bath is used the maximum back pressure on the gas atthe outlet of the die should be increased at the rate of about 21/2 ofwater pressure for each inch of additional aluminum head..

ln the process now being described, it will be seen that gravity is usedto assist in controlling the` coating; Since the wire emerges verticallydownward, the molten aluminum, as the wire leaves the applicator die,tends to form a concentric coating, and: since gravity is pulling thealuminum downwards, a much heavier coating can` be produced on the wirethan would be the case' if the Wire were to emerge from the moltenaluminum` bath' horizontally or upwardly.

In order to assist the formation of a concentric coating it has beenfound that a oating die has advantagesV over a die that is fixed orstationary. One form' of floating die arrangement is shown in FIG. 2. Itcomprises a centrally apertured die member mounted for limited lateralmovement within a cylindrically shaped cage 7i) which is secured instationary fashion to the bottom refractory liner wall 71 of thefurnace. The cage has av central cylindrical inverted cup-shaped space'72' of a diameter larger than the outside diameter ofthe cylindricallyshaped die' 55a. The cage has an inwardly extending annular shoulder 73which provides an opening 74 inthe upper'end of the cage. This shoulder'serves as -a retainer member to coniine the extentV of vertical movementof the floating die 55a which normally rests upon the upwardlylextending hollow boss 75 inthe bottom wall '71 of thecoating section 53of the aluminum pot. The iioating die 55afhas a central cylindricallyshaped diev hole 56a, a bevelledhollow throat portion 76 at its upperend and a flared eXitportion 77 at its lower end. lt will be observedZthat the wire W11 travels downwardly through the pipe section, throughthe central opening 'id` of the cage, then through the die hole 56a intopipe section 62, in which hydrogen' is maintained under pressurecorrespondingV to4 the water head 66 (see FIG. 1). It will now' be seenthat: the die 55a is free to move laterally within a limited, range andvertically within a small tolerance and oats inthe molten aluminum whichenters the cage through opening 74. Hence, if therev is a deviation in'the vertical path of travel of the wire the die will move so that thedie hole 56a will assume a position concentric with the wire, thusaiding in assuring that a concentric coating ofaluminum of uniformthickness is deposited on the wire because the die is self-centering.The gas press re in the pipe 62 puts suhicient back pressure upon themolten aluminum around the periphery of the die to prevent unwantedleakage of the liquid around the die. And, as mentionedabove, the gaspressure is alsoV utilized to control the thickness of coating adheringto the wire.

Another modication of a iioating applicator die arrangement isillustrated in FIG. 3'. ln this arrangement the cage is provided with awire guide arranged above and in vertical alignment with tthe applicatordie. The cage 7h12 comprises a hollow refractory member of generallycylindrical shape secured, by refractory gasket 94a, at its bottom endtothe bottom of the coating section 75-of the aluminum' pot. lts upperend 80 extends above the surface 39 of the molten aluminum. The centralinverted cup-shaped'portion 72b provides a cylindrical space withinwhich is mounted an applicator die 55h similar in shape to die 55a. Ithas an upwardly fiaredk throat 75h, a cylindrical portion 56e, andadownwardly flared exit portion 7'7b. This applicator die may be made: ofa size fittingV snugly within the inverted cupy portion, as shown inFIG. 3. Or the applicator die may be' made to have a diameter as shownin dotted lines 81, smaller than the diameter of inverted cup 72bto'provide a floating die. Horizontally disposed bores 82, 83',` 34connecting with each other and with the molten `aluminum bath' 49 permitentry of the molten aluminum containedr in the potv into the centralkhollow portion of the cage and' thence into the flared throat 761; ofthe applicator die. Mounted within thevertical central opening 854 ofthe cage member-'7013 is a hollow adapter member having an'annularshoulder 87 and a depending guide-retainer portion 8S in which is.mounted a. centrally bored wire guide die S9 resting uponv inwardlyextending annular shoulder 9i?. The upper' end of the adapter is securedby means of a refractory gasket 94' and sealed to the lower end of the'conduit 34, through4 which the wire W10 travels downwardly. ln thisarrangement the wire is` guided bythe centrally bored guide die S9 whichis mounted in vertical alignmentI with the' central boreV Sec ofapplicator diei 55h. The guide die 89 is made of a suitablewearresisting material suchy as tungsten carbide. The die, as shown ismade of tungsten carbide sold under the name Carboloy; The guide die isadvantageous because it insures that the running position of the Wire asit travels downwardly is kept in a' vertical path. The lining for thealuminum furnace and other parts of the apparatus withv which. themolten aluminum comes into contact shouldv be made of a material-whichis not soluble inthe aluminum so that the coating is contaminated tominimum extent by such metals as iron and silicon. In this connectionsuitable materials for the aluminum pot are silicon carbide bonded withsilicon nitride, and aluminum oxide refractories. Suitable materials forthe applicator and guide dies are tungsten carbide, aluminum oxiderefractory, certain silicon carbides, and oxidized Type 304 stainlesssteel. Silicon carbide bonded with silicon nitride has been found tohave advantages as a material for constructing the pot and applicatordie and the related apparatus.

One of the problems in coating steel wire with 'aluminum is caused bythe fact that there is likely to be a very rapid formation of a brittlealuminum-iron alloy at the interface between the aluminum and the steel.If this alloy layer is too thick it will crack when the wire is bent andcause spalling of the coating. Also, if the coated Wire is subsequentlyto be reduced in diameter by drawing through dies, the alloy layer, iftoo thick, will crack and cause the coating to peel off. In order toovercome this diiculty it has heretofore been common practice in the artof coating steel wire with aluminum, to alloy the aluminum applied as acoating with 3% to 5% of siliconwhich markedly reduces the rate offormation of the aluminum-iron alloy layer.

The thickness of the aluminum-iron alloy layer also depends upon thetime allowed for its formation. This time includes the time in themolten aluminum bath and the time after emerging from the bath until thecoating is solidified. According to one feature of the process of thisinvention, the time that the wire is in the molten aluminum is veryshort due to the fact that the depth of the bath is only a few inchesand the time until the coating solidies is reduced by cooling the wireunder controlled conditions after it leaves the aluminum coating bath.In the apparatus, as shown in FIG. l, the wire is given a preliminarycooling in the pipe G2 and then is further cooled to insure desiredsolidication in the water bath 64 in tank 65. The usual operating speedfor the process is a controlled linear speed within a range of from 60to 300 f.p.m. (feet per minute). Thus, for example,- at a speed of 120fpm., or two feet (2') per second, and an aluminum coating bath twoinches (2) deep and a distance of three feet (3') from the aluminum bathto the water bath, the time of the wire in the aluminum bath isone-twelfth (1/12) second and the time from the aluminum bath to thewater bath is one and one-half (l1/z) seconds and these times are soshort that the aluminum-iron alloy layer that is formed is less than.0004" thick and usually in the neighborhood of .0002 thick when usingpure aluminum for the coating material. Consequently the process iscapable of producing pure aluminum coatings on steel wire which aresuiiiciently ductile to permit the coated wire to be wrapped on its owndiameter without spalling the coating. Furthermore such a coated wiremay be cold drawn through dies of smaller diameter without stripping oithe coating.

It has been found that the appearance of the coating depends upon therate and manner of cooling. Hence, it is important in practicing theprocess to control the ternperature of the water bath in tank 65 so thatthe surface of the coating will have a desirable smooth and shinyappearance. With the arrangement as shown in FIG. 1, it has been foundthat, if cold water, say at a temperature somewhat below 90 F. is used,the surface of the aluminum coating has a cratered appearance whereasattemperatures above about 90 F. the surface becomes smooth at about 115F. and above this temperature the surface produced is smooth and shiny.At temperatures higher than about 115 F. the coating may still be liquidor at least too soft by the time the coated wire W13 reaches the guidesheave 92 in the water bath. In such case the guide sheave is arrangedto allow the wire to have further time in the coolant before reachingthe sheave. The guide sheave is mounted for rotation in a position tocause the wire to travel vertically through the aluminum pot and pipe62. The time of exposure of the wire cit 8, W13 to the cooling water 64may be regulated by raising or lowering the position of the guidesheave. However, 'there is an upper limit for the water temperatureabove which the cooling of the wire and adhering aluminum 'coating istoo slow for practical use. Consequently, it has 'been found desirableto control and maintain the temperature of the water cooling bath at atemperature within the range of to 200 F. After passing over therotatable guide sheave 93, the aluminum coated wire is taken up by anysuitable arrangement, such as rotatable :receiving block 12.

A modified form of apparatus for water cooling the coated wire isillustrated in FIG. 4. In this arrangement the wire from the applicatordie passes through a hydrogen-containing pipe 62a, corresponding, ingeneral, to pipe 62 of FIG. 1. Pipe 62a extends into a Water tank adistance below the surface 102 of water 103 in the tank at leastsuflicient to provide the maximum head of hydrogen which it is intendedto use in pipe 62a. A hydrogen inlet nipple 63 is provided which isconnected to a source of hydrogen under pressure. An outlet nipple 63ais connected by a conduit 104 to a tube 105 which extends into apressure-regulating tank 106 below the surface 107 of water therein by adistance d. The outlet of tube is adjusted to a distance a' below thesurface of the water which will provide an adjusted pressure of hydrogenwithin the tube 62a corresponding to distance d as desired and the tubemay be held in adjusted position by clamp 108. As mentioned above thepressure is regulated in pipe 62a to control thickness of coatingapplied to the wire.

The tank bottom is provided with an outlet nozzle 109 in verticalalignment with pipe 62a. Water may flow from tank 101 through thenozzle, through which also passes the coated wire W12 which is cooled bythe water as the wire passes through the tank 101. Water from nozzle 109is caught in a sump tank 110. A water pump 111 takes suction from thetank 110 through suction pipe 112 and circulates it back to tank 101through discharge conduit 113, through a water heater 114, thencethrough conduit connected to the tank. Make-up cold water is suppliedthrough a pipe 116 having a manually operated valve 117 and a solenoidvalve 118 which is operated automatically by a thermostatic controller119 connected to the valve 11S and a temperature sensor 120 in the waterin cooling tank 101. An overflow pipe 121 maintains a constant level ofwater in tank 101; the overow passing into sump tank 110 which isprovided with an over- :tiow pipe 122 which carries away superuouswater. Thus the temperature of the cooling water in tank 101 may beadjusted and kept constant at desired temperature. In order to promotethe formation of a smooth coating, the tank is provided with a verticalbaie 123 terminating at its upper end below the surface 102 of the water103 and at its lower end above the bottom of the tank to reduceturbulence of the water yin the section of the tank through which thewire passes.

The coated wire after passing through nozzle 109 is carried over arotatable sheave 124 to a reel, such as take-up block 12, as shown inFIG. l.

The appearance of the coating also depends upon the nature of the gas inpipe 62. If air is used a rough and poor-appearing coating may result;if a non-oxidizing gas, such as hydrogen, is used a bright-appearingcoating can be obtained. Other suitable gases for obtaining a brightcoating include nitrogen, argon, helium and air from which the oxygenhas been removed.

An alternative apparatus and method for freezing the aluminum coating onthe wire, after the wire leaves the applicator die is illustrated inFIG. 5. In this method the coated wire after it passes through thehydrogen gas in vertical pipe 62, depending from the aluminum pot, isfurther cooled in a vertical water column supported by water flowingthrough an annular orifice. Apparatus for doing this, as shown in FIG.5, comprises a water cooling tank 200 into which extends thehydrogen-containing pipe 62 which depends from the aluminum pot (seeFIG. 1). As shown the tank 200 has a cylindrical side wall 201 and anopen upper end 262. The water tank 2% is mounted concentrically withinan overflow water tank 203 providing a reservoir. The reservoir tank 293has an open upper end 204 and a bottom closure wall 295 having a centralopening 206 from which depends a hollow neck portion 207. Mounted on thehollow neck is a. jet or nozzle device 298; As shown, this nomle devicecomprises a T, similar to a .pipe T, having .a hollow body portion 209from which extends upwardly one leg 210 of the T and from which extendsdownwardly another coaxial leg 211 and from which extends outwardly thethird leg 21.2 of the T. A centrally apertured plug 213 is secured inthe hollow leg 210;. The Iplug has a cylindrical bore 214 terminating inan outwardly flared end 215. The upper end of the bore is, securedl tothe depending hollow neck 207 of the cooling tank 200 in axial alignmenttherewith. Extending into and secured to the lower leg 211 of the T is ahollow plug 215 having an upwardly extending nipple portion of smallerdiameter than the hollow body 209 of the T. The nipple 217 at its upperend terminates in a taperededge 21S compl.,- rnentary to the ared hollowportion 21S of the upper plug 213, this tapered edge terminaing short ofthe ii'ared wall 215. The lower plug has a central bore 19 in axialalignment with the bore 21d of the upper plug. Hence, there is providedan annular orice 2211l between the upper and' lower plugs; this oriceextending upwardly and inwardly toward the vertical axis of the alignedbores 214, 219. Consequently the wire W12 may pass vertically downward'from the applicator die in the aluminum pot, through4hydrogen-containing pipe 62, through cooling water 221 in the watertank and thence through the bores 214 and 219:.

The bottom wall 205 of overiiow-reservoir tank 203 has: an outlet port222, connected to the intake conduit 223` of a suitable pump, such as acentrifugal pump 224. The pump discharge is connected to a dischargepipe 225, in tum connected to water heaterV 226 through which waterpumped from overiiow tank 206 by pump 224 is forced. Water passedthrough heater 226 passes through a` connecting discharge conduit 227?into the hollow body portion 209 of the T 208; a hollow plug 22Sconnecting the conduit 227 to the third leg 212 o the T. The outer orreservoir tank 203- is provided with an overflow drain pipe 229, theupper end of which is open and may be vertically adjusted to` maintain aconstant water level in reservoir tank 203'y at any desiredk height.

Cold water, as needed,V may be supplied to the water cooling systemthrough a pipe 23) connected to a suitable source (not shown). Thesupply pipe 230 is provided withl an openable and! cl'oseable manuallyoperated valve 231 and a solenoid operated' valve 232. The supply pipe230 discharges into. tank 203. The solenoid valve may be automaticallyoperated ttutough-` a; thermostatic control operative in response tochanges inA temperature; of the water in tank 203A through aheat-sensing device 233V connected: through settahle thermostat 234electrically corn nected by suitable wiring 235, to the. solenoid valvein a knowny manner. Hence, the; temperature of the water 221 whichcirculates through the nozzle device 298Y and thercooling tank 200 maybe maintainedI at desired' operating temperature.

It may now be observedfrom the foregoing description that water inoverflow reservoir 203` is pumped through heater 225through the annularorice, 226, upwardly through bore 214, into-Water cooling chamber 201.The water then ows over the top endv 262 of the cooling tank intoreservoir 203; The water is forced through the annular oriiice 220 undersufficient pressure that the velocity head or pressure of the water inan upward direction in bore 214, is sulcient to support the hydrostatichead of theV column of water above the orifice so that the 'waterwillnot' fall by gravity into bore 219 while the coated wire W istravelling downwardly therethrough from the .aluminum pot which is, ashereinbefore described, located above the hydrogen-containing pipe 62.

The temperature of the water is controlled by thermostat control 234which is set to open solenoid valve 232 to admit cold water to thesystem whenthe water gets too hot. Also heater 226 may be used, ifdesired', to aid in adjusting the Water temperature ir it is too cold.Excess water flows `out from overilow pipe 229.

This unit of the apparatus as illustrated in FIG. 5, causes the coatedwirev emerging from pipe 62 to be cooled by a column of water from thetop of cooling tank 206 tov the annular oriiice 22h. Such an arrangementmay be used when it is desired to heat-treat high carbon wire for wireYdrawing of the aluminum coated wire. In this case the wire is heated inhydrogen prior to passing it through the aluminum coating bath, whichoperation may be carried out in apparatus such as illustratedv inFIG. 1. However, the cooling system, as illustrated in FIG. S, is usedin place of the water tank arrangement illustrated in FiG. l. The wireis heated in hydrogen to above the critical temperature (1350o F.) totake the carbides into solution', it is then cooled to approximately thetemperature of the moltenv aluminum bathI (about 12"'5" F.) and thencoated with molten aluminum as described above. The coated aluminum wireis then cooled' to 1G00" to l=l5tl F. by the wat-er 221 in tank 201which is circulated as described in connection with the apparatus ofFlG. 5, after which the coated' wire emerges from bore 219 into theatmospheric air. At this ternperature (l0G0'-1l50 F.) the aluminumcoating is solid and` the carbides on exposure to the temperature of theatmosphere' come out of solution as very tine pearlite, producing whatis known as a patented structure. The purpose of' having the coated wireemerging into atmospheric air after leaving the water cooling device ofFIG. 5, is to retard the rate oi cooling to allow time for the carbidesto come out of soiution'. The time required is in the neighborhood ofl() seconds so it is desirable that the coated wire W14 is not cooledvmore rapidly thanv by exposure to atmospheric air for thisv length oftime. The air patented aluminum coated wire W14' may then besubsequently wire drawn', through suitable dies to desired smaller dianeter.

Apart from the. desirability of patenting for further wire drawing, itisY to be. pointed out that ifV high carbon wire (carbon over 6.35%)were heated' above the critical temperature. (l350 F.) inA hydrogen andthen aluminum coated andl subsequently Icooled in water as described inconnection with tank 65, FlG. l, it would become brittle and might breakinstead or" passing around pulley 92. Consequently the arrangement asshown' in' FIG. 4 or in Fl'G. 5 is very advantageous when it is desiredto prevent embrittlement of high carbon wire where it is heated abovel35(`1`o F. in hydrogen tunnel. 31 (see FIG. l).

All alternate way of processing high carbon wire is to (a) heat theVwire to below l350 F. (the critical temperatures) inthe hydrogen tunnelY31. Inl this case cooling in water willA not cause brittleness. Anotherway is to cool in air (or hydrogen) after emerging. from the aluminumbath 4d untilv the temperature is not higher than 1G00 F. In thisalternative, the water cooling would bel omitted altogether andsuiiicient distance would be provided between thel aluminum pot andguide pulley 92 (FIG. l) to permit the requiredA cooling prior towinding the wire on takeup block 12. But this method has thedisadvantage of allowing' more time for an undesirable thickness ofaluminum-iron alloy layer to form at the interface between they outsidealuminum Icoating layer and the surface of the wire.

Other coating metals than aluxninurnrriayl be used for coating metalproducts in accordancewith certain' featuresY of the process of theinvention. The process lends itself to the use of aluminum siliconalloys in the. coating bath, and the process is particularly suitablefor coatings of zinc since this metal forms a brittle Zinc-iron alloy ina manner analogous to the formation of an aluminumiron alloy whenaluminum is used as the coating. In the case of zinc, the operatingtemperature of the molten zinc coating bath should be about S5 0 insteadof about l275 the temperature adapted for the aluminum coating bath.Also in the case of zinc sufficient distance should be provided betweenthe wire heating zone and the molten zinc bath or coating zone to permitthe wire temperature to drop to about 850 when it enters the molten zincbath. The process also may be used for coating other metals than steelwith a coating other than aluminum or zinc. Although the process hasbeen described in detail in connection with the coating of steel wire byway of illus trative example, it will be understood it may be used forcoating strip or any body of elongate character of uniform cross sectionwhich may be caused to travel as a continuously travelling wire orstrip. Accordingly, it will be understood than when the term strand isused in the claims it is intended to include wire and strip. Also, theprocess is adapted for coating various kinds of elongate metal productswhich can be alloyed with a coating metal such as wire or strip made ofcopper, stainless steel and the like.

While there has been disclosed herein, for purposes of illustration, oneWay of treating the strand for the application of the molten coatingmetal, it will be understood that other treating methods may be usedprior to applying the molten coating metal; the significant point beingthat the surface of the strand must be thoroughly clean and free fromoxide or other contaminants when the strand is passed through the metalcoating bath. For example, the wire or strip may be cleaned and coatedwith a flux prior to coating; or any other means known in the art forcausing molten coating metal to coat a travelling metal strand may beused. Also, in some instances, certain features of the invention may beused in an arrangement whereby the strand may be caused to travelhorizontally, vertically upwards or at an angle through the die, in amanner such that a confined fluid gas pressure may be exerted againstthe outlet end of the die for controlling coating thickness.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described or portions thereof, but it isrecognized that various modications are possible within the scope of theinvention claimed. In the claims the term downstream will be understoodto mean the direction of travel of the strand and the term upstream, theopposite direction.

What is claimed is:

1. In a process of coating a metal strand with a coating metal whereinthe strand is continuously passed through a molten bath of the coatingmetal, the method of controlling the thickness of the coating metalapplied to the strand which comprises continuously passing the strandthrough a die positioned in the body of said bath of molten metal andhaving an orice diameter greater than the diameter of the coated strandand thence through an enclosed elongate chamber having one endcommunieating with the die oritice and owing molten coating metal bygravity flow in a downward direction from said molten bath through theannular space between said die and strand in the direction of travel ofsaid strand whereby to apply coating metal to said strand andcontrolling the amount of coating metal applied to said strand as itemerges from said die by a controlled positive static gas pressuremaintained within said chamber and exerted against the outlet end ofsaid die in a direction opposite the direction of travel of said strandand at the same time not permitting gas within said chamber to flowthrough said die.

2. A method according to claim 1 in whichY said strand as it emergesfrom said die is passed through a chamber communicating with the outletend of said die at one end and with a liquid cooling bath at the otherend in which a non-oxidizing atmosphere is maintained to exert saidcontrolled pressure against the outlet end of said die and the coatedstrand is passed through said non-oxidizing atmosphere into and throughsaid liquid cooling bath to cool said coated strand, while maintainingsaid cooling bath at a temperature to insure that the cooled coatedstrand emerging from said cooling bath has a smooth surface.

3. A method of coating a metal strand with a metal coating whichcomprises treating a continuously travelling length of said strand torender its surface amenable to alloying said coating metal therewith,passing the so-tre'ated continuously travelling strand through anapplicator die having an oriiice communicating with a molten'bath ofsaid coating metal and having a diameter greater than the diameter ofthe coated strand so that there is an annular space of predeterminedsize around said strand as it travels through said die, causing moltencoating metal to iiow by gravity from said bath through said annularspace in the direction of travel of said strand, thereby applying acoating of said molten metal on to said strand, continuing the movementof said strand through an enclosed elongate chamber communicating withsaid annular space at the outlet end of said die and controlling thethickness of coating adhering to said strand as said strand passes intosaid chamber by maintaining a controlled positive static gas pressuremaintained Within said chamber whereby only a controlled static gaspressure is exerted against the molten metal in said annular space atits outlet and at the same time maintaining the pressure sutlicientlylow in said chamber to prevent any of said gas from owing through saidapplicator die in a direction opposite the direction of travel of saidstrand.

4. A method of coating a steel strand with a metal coating such asaluminum and aluminum alloys which comprises treating a continuouslytravelling length of said strand to render its surface amenable toalloying said coating metal therewith, passing the so-treatedcontinuously travelling strand in a downward direction through an.applicator die having an orifice communicating with a molten bath ofsaid coating metal through which said strand passes and a diametergreater than the diameter of the coated strand so that there is anannular clearance space of predetermined size around said strand as ittravels through said oriiice, causing molten coating metal to ow fromsaid bath in a downward direction through said annular space in thedirection of travel of said strand in contact with the surface of saidstrand, thereby applying a coating of said coating metal to said strand,continuing the movement of said strand having the molten coating metalapplied thereto downwardly .through an elongate chamber communicating atits upper end with said annular space at the outlet end of said die andclosed at its lower end by a liquid seal and controlling the thicknessof the coating adhering to said strand as it emerges from said die bymaintaining a gas under controlled positive pressure in said chamberwhich exerts only a static pressure against the outer end of said die atsaid annular space in a direction opposed to the direction of travel ofsaid strand, and cooling said coated strand after it emerges from saiddie to solidify said coating metal.

5. A method according to claim 4 in which a nonoxidizing gas ismaintained in said chamber for exerting said gas pressure against theoutlet end of said die and to provide a non-oxidizing gas through whichthe coated strand passes and is cooled after it emerges from said die.

6. A method according to claim 5 in which the strand as it emerges fromsaid chamber is passed throughtan aqueous cooling bath maintained at acontrolled temperature adjusted to insure that the coated strand emerg-13 ing from said cooling bathv has aA smooth surface7 solidifiedcoating.

7. A method according to claim 6 in which the gas maintained underpressure in: said chamber is hydrogen and said liquid cooling bath iswater between- 90 F. and ZG" F. and maintained at a temperature whichinsures both a smooth coating and a bright appearing surface.

8. A method according to claim 7 in which the diameter of the dieorifice through which the strand passes is within the range of 7% to 21%larger than the diameter of the strand.

9. A method according to claim 8 in which the time of travel of thestrand from the time it is brought into contact with the molten coatingmetal to the time it reaches said water cooling bath is notsubstantially greater than 2 seconds.

19. A process for producing a steel wire coated wlth a coating metalsuch as aluminum and aluminum alloys capable of being reduced indiameter by drawing through dies without cracking or peeling the coatingmetal which comprises heating a continuously travelling length of highcarbon steel wire, after it has been cleaned, to a temperature above1350 F. at which the carbides in said steel go into solution andremoving any oxides present on the surface of said wire, causing saidwire to travel through a molten bath of said coating metal maintained ata temperature about 1275 F., applying a predetermined thickness ofmolten coating metal to said strand by passing said strand through anapplicator die having an orifice mounted in communication with saidbath, said orifice having a diameter greater than the diameter of thecoated wire, then passing the coated wire through a confined atmosphereof non-oxidizing gas maintained under positive pressure which is exertedas static pressure against the outlet end of said applicator die orificeand adjusted to control the thickness of molten coating metal adheringto said wire, causing said coated wire to travel through said confinednon-oxidizing atmosphere and thence through a water bath maintained at atemperature to cool said coating to a temperature between 1000 F. and115 0 F. thereby solidifying said coating metal and then cooling saidcoated wire at a rate to cause the carbides to come out of solution asvery ne pearlite.

11. A process for producing a steel wire coated with a coating metalsuch as aluminum and aluminum alloys capable of being reduced indiameter by drawing through dies without cracking or peeling the coatingmetal which comprises heating a continuously travelling length of highcarbon steel wire, after it has been cleaned, to a temperature above1350 F. at which the carbides in said steel go into solution, removingany oxides present on the surface of said wire by passing it through asurrounding atmosphere of hydrogen in communication with an aluminummetal coating bath maintained molten at about 1275 F., cooling said wireto about the temperature of said coating bath while still surrounded bysaid hydrogen atmosphere, then causing said wire to travel downwardlythrough a molten metal applicator die having an orifice the diameter ofwhich is larger than the diameter of said wire by at least 7% but notmore than 21% so that there is an annular clearance space ofpre-determined space in said die surrounding the wire, which annularspace at its entrance end is in communication with said molten metalcoating bath, causing said molten coating metal to ilow by gravity in adownward direction through said annular space in contact with the wireas the wire passes through said orifice thereby causing the molten metalto adhere to said wire, then passing the coated wire as it movesdownwardly through an elongated chamber communicating at its upper endwith said annular space and containing a confined atmosphere ofnonoxidizing gas, maintained above atmospheric pressure, which isexerted as positive static pressure against the outlet end of saidannular space and adjusted to control the thickness of molten coatingmetal adhering to said wire, causing said coated wire to travel throughsaid nonoxidizing atmosphere and thence through a water bath and thereincooling said coating to a temperature between 1000 F. and 1150` F.thereby solidifying said coating metal' and. then. further cooling saidcoated wire at a; rate to cause the carbides in the steel wire to comeout. of solution as very line pearliter 12i Apparatus for coat-ing ametal: wire strand of given diameter with a coating metal comprisingmeans for cleaning the` surface. of a continuously moving length ofstrand travelling in a direction herein designated as downstream, afurnace having a pot holding a molten bath of said coating metalpositioned downstream from said cleaning means; heating means positionedupstream from said molten bath to heat said wire strand; means forapplying molten coating metal to said heated strand which comprises anapplicator die having a cylindrical orilice through which said strandtravels, said orifice having a diameter greater than the diameter of thecoated strand of given diameter whereby an annular clearance space ofpredetermined area is provided in said die around said strand as ittravels through said orice, said die being mounted on the bottom wall ofsaid pot with the upstream end of said annular space communicating withsaid bath and in such position that molten coating metal tiowsdownwardly by gravity from said bath through said yannular space in thedirection o ftravel of said strand and in contact therewith as saidstrand travels through said orifice, means defining an enclosed gaschamber positioned downstream from said die and connected to providecommunication between said chamber and said annular space at itsdownstream end whereby gas pressure within said chamber is extertedagainst the downstream end of said annular space; means of introducinggas into said gas chamber under pressure; gas pressure regulating meansto maintain a regulated positive pressure within said gas chamberwhereby a controlled static gas pressure is maintained against moltenmetal fiowing downwardly in said annular space around said wire tocontrol the thickness of molten metal coating applied to said wire as itpasses through said die orifice; and means positioned downstream fromsaid chamber for cooling the coated wire.

13. Structure according to claim 12 in which said applicator die ismounted for floating lateral movement and a cage surrounds said diepreventing substantial longitudinal movement of said die and limitingthe distance of said lateral movement.

14. Structure according to claim 13 which includes guide means causingsaid strand to travel through said molten metal coating bath and diedownwardly in a substantially vertical direction, and said gas chamberis mounted in vertical alignment with said orifice downstream from saidapplicator die.

15. Structure according to claim 14 which includes a guide member havingan opening therein through which said strand passes in a downwarddirection, said guide member being connected to said cage and mountedupstream from said applicator die with said opening in alignment withthe orifice of said applicator die and said gas chamber is mounted invertical alignment with said orifice downstream from said applicatordie.

16. Structure according to claim 14 in which the means for cooling saidcoated strand downstream from said gas chamber comprises a tank having abottom mounted below said gas chamber and containing a moving coolingliquid, means having a cylindrical wall defining an elongate hollow borebelow said tank through which said strand passes downwardly in asubstantially vertical direction and vertically aligned with said gaschamber, an annular opening in said cylindrical wall providing anupwardly and inwardly extending annular nozzle and liquid pumping meansconnected with said nozzle adapted to force water through said nozzleupwardly through 15 said bore and tank in a direction counter to thedirection of travel of said wire therethrough with suiicient force toprevent substantial ow of liquid downwardly in said bore below saidnozzle.

17. Apparatus according to claim 16 in which said cooling tank issurrounded by a reservoir into which cooling liquid forced through saidtank overows and said pumping means is connected to take suction fromsaid reservoir and circulate the cooling liquid back through saidnozzle. Y

18. Apparatus according to claim 17 which includes means forautomatically controlling the temperature of the cooling liquidcirculated through said cooling tank.

References Cited bythe Examiner UNITED STATES PATENTS Underwood 118-420X Girard et al.

Cook 118-68 X Dahlstrom.

Keller 11868 X Nystrom.

Knapp 118-125 X Stalson.

Eliot 22-200.1

RICHARD D. NEVIUS, Primary Examinar,

4. A METHOD OF COATING A STEEL STRAND WITH A METAL COATING SUCH ASALUINUM AND ALUMINUM ALLOYS WHICH COMPRISES TREATING A CONTINUOUSLYTRAVELLING LENGTH OF SAID STRAND TO RENDER ITS SURFACE AMENABLE TOALLOYING SAID COATING METAL THEREWITH, PASSING THE SO-TREATEDCONTINUOUSLY TRAVELLING STRAND IN A DOWNWARD DIRECTION THROUGH ANAPPLICATOR DIE HAVING AN ORIFICE COMMUNICATING WITH A MOLTEN BATH OFSAID COATING METAL THROUGH WHICH SAID STRAND PASSES AND A DIAMETERGREATER THAN THE DIAMETER OF THE COATED STRAND SO THAT THERE IS ANANNULAR CLEARANCE SPACE OFPREDETERMINED SIZE AROUND SAID STRANDAS ITTRAVELS THROUGH SAID ORIFICE, CAUSING MOLTEN COATING METAL TO FLOW FROMSAID BATH IN A DOWNWARD DIRECTION THROUGH SAID ANNULAR SPACE IN THEDIRECTION OF TRAVEL OF SAID STRAND IN CONTACT WITH THE SURFACE OF SAIDSTRAND, THEREBY APPLYING A COATING OF SAID COATING METAL TO SAID STRAND,CONTINUING THEMOVEMENT OF SAID STRAND HAVING THE MOLTEN COATING METALAPPLIED THERETO DOWNWARDLY THROUGH AN ELONGATE CHAMBER COMMUNICATING ATITS UPPER END WITH SAID ANNULAR SPACE AT THE OUTLET END OF SAID DIE ANDCLOSED AT ITS LOWER END BY A LIQUID SEAL AND CONTROLLING THE THICKNESSOF THE COATING ADHERING TO SAID STRAND AS IT EMERGES FROM SAID DIE BYMAINTAINING A GAS UNDER CONTROLLED POSITIVE PRESSURE IN SAID CHAMBERWHICH EXERTS ONLY A STATIC PRESSURE AGAINST THE OUTER ENDOF SAID DIE ATSAID ANNULAR SPACE IN A DIRECTION OPPOSED TO THE DIRECTION OF TRAVEL OFSAID STRAND, AND COLING SAID COATED STRAND AFTER IT EMERGES FROM SAIDDIE TO SOLIFIGY SAID COATING METAL.